Alfred Kastler

Educated at the École Normale Supérieure in Paris, Kastler conducted optical and atomic physics research under Pierre Brossel. In 1950, he developed the technique of optical pumping, using polarized light beams to manipulate the quantum population of energy levels in atoms.

Optical pumping provided the essential theoretical and experimental breakthrough that allowed Townes and Maiman to develop the laser and maser, and made possible ultra-precise atomic rubidium and cesium clocks. A passionate pacifist, poet, and European federalist, he served as President of the French League for Human Rights.